Introduction

Background and rationale

Sedentary behaviour, physical activity and health in children

Childhood is a critical period for the establishment of healthy lifestyle behaviours, including physical activity. Continual advances in modern technology, economic progress and changes to our environments have resulted in reductions in physical activities associated with daily living, and in sedentary behaviour becoming ubiquitous within all settings of daily life. Sedentary behaviour is a behaviour distinct from physical (in)activity and is currently defined as ‘any waking behaviour characterised by an energy expenditure of ≤ 1.5 metabolic equivalents (METs) while in a sitting, reclining or lying posture’.1 Although reclining and lying postures are included in the definition, most of the time an individual (young people and adults) spends sedentary will be in a sitting position during waking hours. Participation in regular physical activity has numerous short- and longer-term physiological, psychological and social benefits for young people.2–4 For example, reviews have shown that physical activity can improve blood pressure, weight status and bone mineral density, and lead to improvements in self-esteem and depression, and, in the longer term, can prevent chronic disease.2,4 It is acknowledged that physical activity is beneficial to health, and sedentary behaviour has been shown to adversely affect health.

Sedentary time is associated with an increased risk of metabolic syndrome,5 cardiovascular disease,6–8 type 2 diabetes mellitus,7,8 all-cause mortality9 and depression10 in adults. Although the evidence for associations between objectively assessed sedentary time and health outcomes in young people is less consistent,11–13 the proxy sedentary behaviours of television viewing and screen time (the most prolific area of sedentary behaviour research) are unfavourably associated with body composition, fitness, self-esteem, cognitive development, pro-social behaviour, academic achievement in children13,14 and cholesterol in adulthood.15 Sedentary behaviours in children have, furthermore, been shown to coexist with lower levels of physical activity16 and other ‘unhealthy’ behaviours, such as increased consumption of energy-dense foods, lower intakes of fruits and vegetables,17 and inadequate sleep.18 Furthermore, recent evidence suggests an association between sedentary behaviour and several markers of inflammation and endothelial dysfunction,19 signalling potential mechanistic links with poor cardiovascular health in children. In addition, the emergence of an increased cardiometabolic health risk profile in some population groups is evident during the first decade of life.20 For example, British South Asian children have demonstrated higher levels of glycated haemoglobin, fasting insulin and triglycerides, and lower high-density lipoprotein cholesterol than white British children, as well as having a higher sum of all skinfolds and fat mass percentage.21,22 Therefore, these populations may be more vulnerable to the adverse affects of excessive sedentary time. Indeed, evidence of the influence of sedentary behaviour on the health of young people has prompted many countries to establish public health recommendations for sedentary behaviour. The UK, USA, Canada, Australia and the Netherlands, for example, now recommend that young people should reduce sitting time and break up long periods of sitting as frequently as possible.23–27

Prevalence of sedentary behaviour in children

In the UK, sitting is the most prevalent behaviour exhibited during waking hours in children, accounting for > 65% of their waking time (or 7.5 hours),28 with some children reportedly sitting for > 10 hours per day (> 70% of waking hours).29 Accelerometer data from the Health Survey for England have shown that young people (aged 5–15 years) spend, on average, 7 hours per day sedentary.30 International research shows similar prevalence rates, with data from the International Study of Childhood Obesity, Lifestyle and the Environment (ISCOLE)31 showing that children across 12 geographically and culturally diverse countries spend an average of 8.6 hours per day sedentary.31 Similar proportions of waking hours spent sedentary have also been reported in children and adolescents from Canada and the USA.32,33

Objective (accelerometry) sedentary behaviour data further suggest that children spend the majority of their school time sedentary.34,35 For example, in children aged 10–12 years, across five European countries, 65% of the time spent at school was sedentary.35 More recently, research has turned to inclinometer devices to more accurately measure total sedentary time (or sitting specifically), with data from these devices from British, Australian and Malaysian children (aged 8–12 years) further confirming that the majority of their time at school (70–71%), on weekdays (53–69%) and weekend days (60–73%) is spent sitting.29,36–38

The rising prevalence of sedentary behaviour (and sitting) is of further public health concern because this behaviour in childhood has been shown to increase across key transitions in children’s lives (i.e. from primary to secondary school),39 and has been shown to track into adolescence40 and adulthood.15 Given the physiological and psychosocial risks related to sedentary behaviour, and the evidence that sedentary behaviour increases as children get older, there is a need for interventions to reduce sedentary behaviour and increase movement in children.

Interventions to reduce sedentary behaviour in young people

The environments and social norms that children are exposed to have dominant influences on their activity behaviour. Given that children spend half of their waking hours at school, it is plausible that the school environment may be a critical influence on their health behaviour patterns41–43 and be a most appropriate target environment for interventions. A plethora of physical activity interventions aimed at young people have been conducted over the past two decades.44,45 School-based interventions promoting physical activity have been successfully implemented during physical education classes, break times and before and after school hours, and have revealed positive effects on physical activity.44 Furthermore, there is now growing evidence supporting the use of physical activity as a teaching tool (e.g. physically active learning) and classroom movement breaks, as a means of facilitating classroom management, student attention and focus on task.46 However, teachers, education departments and organisations frequently cite a crowded curriculum, alongside other barriers, such as lack of knowledge or confidence, as reasons for not implementing physical activity programmes. Thus, alternative methods that do not add to teachers’ workload and require minimal specialist knowledge are required.

With an increasing interest in sedentary behaviour, a number of systematic reviews and meta-analyses have been published, synthesising the interventions that focus on young people.47,48 Although most interventions specifically targeting sedentary behaviour have been home or school based, sedentary behaviour has typically been targeted as screen time and via behaviour change strategies within non-school settings (i.e. screen time at home),48 the effects of which have been inconclusive.47 Most interventions specifically targeting sedentary behaviour have not been based on a behaviour change framework or theory.48 In a recent review of interventions targeting sedentary behaviour, only 10 out of 21 interventions included studies that were theory based.48 Theoretical frameworks provide a scaffold for intervention development from being an evidence-based source for understanding the behaviour of interest and possible levers of change,49 allowing a systematic evaluation of the intervention outcomes. Theories and frameworks typically utilised in sedentary behaviour interventions to date, again which have largely targeted screen time, include social cognitive theory, behavioural choice theory, the social ecological model and the chronic care model.48

Although there is an abundance of behaviour change theories, models and frameworks for researchers to use (indeed 83 were identified in a recent systematic review49), the behaviour change wheel (BCW)50 has increasingly received attention within the sedentary behaviour literature.51,52 The BCW synthesises 19 pre-existing frameworks of behaviour change into a single interface, incorporating a theory of behaviour, intervention functions and associated policy categories, and can be applied to any behaviour in any setting.50 As policy can only influence behaviour through interventions, which in turn act through capability, opportunity and motivation, the framework is represented as a wheel with an outer layer (policy categories) influencing the next layer (intervention functions), until behaviour is changed at the very centre of the wheel.50

The capability, opportunity, motivation – behaviour model (COM-B) (sources of behaviour) hypothesises that for specific behaviours to occur, the individual must have both the physical and psychological capability to perform the given behaviour, along with the social and physical opportunity to perform the behaviour, and be motivated to perform the specific behaviour more so than any other behaviours within that moment in time. Within the context of sedentary behaviour, the only interventions that have consistently demonstrated a reduction in sedentary time in younger populations are those utilising a standing desks design within the classroom (i.e. environmental restructuring),53 thus providing a physical opportunity for children to stand and/or break up their sitting time. As children spend up to 6 hours per day in the school environment and owing to the potential reach of school-based interventions to tackle inequalities (i.e. demographic and social/cultural), changing the traditional classroom environment to an activity-permissive one by reducing sitting in this environment (rather than the traditional focus on leisure time screen use) is a promising area of research. Indeed, environmental restructuring to provide a physical opportunity to stand rather than sit would certainly be essential within the classroom environment, as traditional furniture dictates that children spend most of their class time sitting. However, implementing new practices and/or changing existing practices in organisations, such as schools, require changes in individual behaviour (i.e. pupil) and collective behaviour (i.e. teachers/school staff and pupils), and changing behaviour requires an understanding of the influences on behaviour in the context in which they occur. Our understanding of these factors can be enhanced through the theoretical domains framework,54 which provides a theoretical lens through which to view the cognitive, affective, social and environmental influences on behaviour.55

Interventions to reduce sitting within the classroom environment

There are now a growing number of environmental interventions that aim to reduce classroom sitting time and increase standing and movement, which have been implemented in schools and evaluated for effectiveness through systematic reviews.56,57 Feasibility studies, including our own,29,58,59 have demonstrated the effectiveness of incorporating sit–stand desks in primary school classrooms over the short term (< 12 weeks). For example, sit–stand desks have been shown to enable pupils to alternate between sitting and standing without disruption to teaching, learning or behaviour.56 Furthermore, sit–stand desks in classrooms have been shown to be effective in increasing energy expenditure60,61 and standing and movement62 during the school day. In addition, studies have shown that sit–stand desks in classrooms lead to improvements in children’s posture and musculoskeletal comfort,63,64 levels of academic engagement65 and achievement,64 and improved cognitive function.66 Sitting time has been shown to be reduced by between 44 and 60 minutes per day and standing time increased by between 18 and 55 minutes per day during classroom time at school, over 4 and 9 weeks’ follow-up.29,59,67 More recently, the impact of standing desks on sitting time in the classroom has been assessed over 16 weeks’ follow-up, with results suggesting a 13% reduction in sitting and a 31% increase in standing at school, relative to baseline.68 Clearly, incorporating standing desks in classrooms shows great promise for reducing children’s sitting time. However, systematic reviews have concluded that the majority of studies conducted to date have included relatively small samples, have been short in duration, have not included a randomised controlled design and have not assessed the impact of standing desks on academic performance.56,57,69 Further exploration in this area of research is thus warranted.

Development of the Stand Out in Class study

The feasibility of incorporating sit–stand desks in the classroom environment over a 9-week period was demonstrated in an earlier intervention study we conducted with Year 5 Bradford primary school children.29 In this feasibility study, we verified a number of our outcome measures (objectively determined sitting time and physical activity, body composition, blood pressure and teacher-reported pupil behaviour). In a novel approach, we replaced three standard desks (sitting six children) with six sit–stand desks. The teacher rotated the children assigned to the intervention group around the classroom in groups of six, according to the lesson being taught, using naturally occurring breaks between lessons to do so, ensuring that each child was exposed to the sit–stand desks once a day for at least 1 hour. Children in the control group continued with their usual practice, with no environmental changes to their classroom. Reductions in classroom sitting of 52 minutes per day were observed within the intervention group and reductions in total daily sitting of 81 minutes per day on school days after 9 weeks were seen. Teachers reported improvements in behaviour and no perceived negative effects on teaching or learning were observed. As part of this feasibility work, we also compared the changes in classroom sitting observed in our sample with data from a related feasibility study conducted in a primary school in Melbourne, Australia.29 In the Melbourne study,29 every child in the intervention classroom had a sit–stand desk. Despite differences in desk provision, no significant differences in reductions in sitting time were observed between the two studies. Reductions in classroom sitting of 44 minutes per day and reductions in total daily sitting of 68 minutes per day were observed in the Melbourne intervention class. This early work demonstrates the potential of sit–stand desks in the classroom as a way of reducing sitting in children over the short term, irrespective of the type of sit–stand desk provision.

Following this successful feasibility work, the next logical step required was the development of the Stand Out in Class intervention. With the aim of informing a future definitive trial, the Stand Out in Class pilot study was developed to establish procedures for school and participant recruitment, and the acceptability of the intervention and outcome measures, and attrition rates. This intervention was informed by our feasibility work and public and patient involvement (PPI) with teachers and children through informal interviews and workshops (children only), in which our earlier work was described and their feedback on the intervention and proposed measures was obtained. This present study therefore comprises a pilot evaluation of the implementation of standing desks in the classroom through a cluster randomised controlled trial (RCT), with objective measures of sitting and activity, and a range of health- and education-related outcome measures. Rapid increases in sedentary time have been observed in children aged ≥ 11 years, relative to younger age groups.70 This study targets Year 5 classrooms, comprising children just below this age (9- to 10-year-olds), with the goal of reducing the typical rise in sedentary time seen during the transition into adolescence,39 given also that sedentary behaviours track from childhood into adolescence and adulthood.40 Furthermore, evidence suggests that children in Year 5 upwards are active participants in their own learning, making them an optimal target for classroom interventions that may facilitate learning.71 A cluster design is considered appropriate because the intervention is delivered at the classroom level, rather than at an individual level.

Aims and objectives

The aim of this study is to undertake a pilot cluster RCT of the introduction of sit–stand desks in primary school classrooms to inform a future definitive trial.

Pilot trial study objectives

1. Establish and refine a recruitment strategy for schools and pupils.
2. Determine attrition in the trial (schools and children).
3. Determine completion rates for outcome measures (and whether or not these are sufficiently high to provide accurate data in a full trial).
4. Assess whether or not there are any differences in trial recruitment, retention and acceptability between ethnic groups.
5. Assess the acceptability of randomisation to schools.
6. Assess the acceptability of measurement instruments to teachers, children and parents, including the activPAL™ (PAL Technologies Ltd, Glasgow, UK) inclinometer, as the tool for the measurement of the primary outcome.
7. Assess the acceptability of the intervention to teachers, children and parents.
8. Monitor any adverse effects, such as musculoskeletal discomfort and/or disruption to the classroom/learning, to inform the design of a full trial and minimise or eliminate any such effects.
9. Assess intervention fidelity.
10. Derive preliminary estimates of the effect of the intervention on children’s total daily sitting time, physical activity, indicators of health (markers of adiposity and blood pressure), cognitive function, and academic performance, engagement and behaviour.
11. Estimate the standard deviation (SD) of the primary outcome to inform a sample size calculation for a full RCT.
12. Determine the availability and completeness of economic data, and conduct a preliminary assessment of potential cost-effectiveness.